DE102013007932A1 - Scattered light measurement device for inspecting sample surface, has decoupling device and filter converting main beam emitted from sample surface into secondary beam for transmitting original image of illumination spot to camera sensor - Google Patents

Abstract

The device (10) has a camera sensor (28) including upstream converging lenses (22, 24, 26), and a light source (12) for illuminating a sample surface (14) of a sample (16). A decoupling device (58) and a filter (60) converts a main beam emitted from the sample surface into a secondary beam (34) for transmitting an original image (50) of an illumination spot (52) to another camera sensor (48) having a converging lens (42), where a scattering pattern (40) having high-frequency components of a residual beam from the sample surface is transmitted to the former camera sensor. An independent claim is also included for a method for evaluation of measurement data obtained by the scattered light measurement device.

Description

The invention relates first of all to a scattered light measuring device having a first camera sensor with at least three upstream converging lenses and a light source for illuminating a sample surface of a sample to be examined with a parallel light bundle, wherein the sample, the at least three converging lenses and the first camera sensor each spaced from each other along a common optical Main axis are aligned.

Moreover, the invention relates to a method for evaluating the measurement data supplied by the two camera sensors.

From the prior art, a variety of devices and methods for surface inspection of samples of various kinds using the s. G. Scattered light measurement known. In particular, large-scale surface inspections of samples by direct imaging methods, ie, for. B. by means of a macro lens and a camera to make, however, it is necessary to find a compromise between the size of recorded in a measuring step surface section and the achievable resolution, since a high-detail photographic recording requires a very small spot. As a result, the cost of a given total area to be examined increases inversely proportional to the square of the spot diameter. However, only a part of the problem can be solved with the methods of the conventional scattered light measuring technique, since a scattering image meaningful with respect to microscopic structures can be meaningfully obtained only with a measuring spot of a sufficiently large diameter so that the boundary of the measuring spot does not produce a noticeable diffraction effect.

From the DE 10 2009 036 383 B3 a device and a method for angle-resolved scattered light measurement is known, which are also suitable for the measurement of structures in the nanometer range and in the subnanometer range, the device should also have a very compact construction.

In one embodiment of this prior art device, light from a first light source through a lens system as well as a pinhole and a further downstream lens radiate to an examination area of a sample. The light scattered on the surface of the sample falls on a detector. This detector is given by a CMOS sensor matrix and has a microlens array. Any scattered light thrown back by the detector is swallowed by an absorber. In addition, the device has a second light source whose light likewise falls on the examination region of the sample after passing through a lens system. For metrological evaluation, an evaluation unit is provided which is set up for program-technical evaluation of output signals of the detector and z. B. allows the calculation of a roughness of the sample. A disadvantage of this known device lies in the structurally complex detector.

An object of the invention is to provide a scattered light measuring device, which allows with the least possible effort both macroscopic, as well as microscopic properties of a sample surface to be examined -. B. in the context of a large-scale and rapid examination of workpieces or semi-finished products - reliable statements to win.

In addition, an object of the invention is to obtain a method for the evaluation of measured data obtained with the aid of the scattered light measuring device.

This object is initially achieved by a scattered light measuring device having the features of patent claim 1.

Characterized in that at least a portion of an emanating from the sample surface main beam with the aid of a decoupling device and a filter device in a secondary beam for transmitting an original image of the illumination spot to a second camera sensor and a residual beam for transmitting the scattering pattern of the sample surface is split to the first camera sensor, wherein the original image mainly low-frequency components and the scattering image contains substantially high-frequency components and the second camera sensor is preceded by at least a fourth converging lens, in contrast to conventional scattered light measurements of the beam path at a suitable location -. B. by means of a partially transparent mirror - divided into a residual and a secondary beam. From the decoupled secondary beam a defined frequency-limited image of a lighting spot is obtained, so that the scattering image contains only the remaining high-frequency components. As a result, at the same time direct reflections from the scattering pattern are simultaneously suppressed or masked out - a positive side effect which makes an additional beam trap (see "beam dump") necessary in the case of conventional scattered-light measuring devices. In contrast, in the device according to the invention, however, just this proportion is used for image acquisition.

With an appropriately designed optics, an original image of the illumination spot itself is obtained with the aid of the split secondary beam and imaged on a second camera sensor. Preference is given in the beam path measures for Preventing local subsampling of the original image. Furthermore, the scattering can ggfls. be suitably conditioned, z. B. by suppression of direct reflections. The data processing can, for. B. for the scatter and the original image separately, wherein statements about the low-frequency range from the original image and concerning the high-frequency range of the scattering image in the sense of a data fusion are derived. The camera sensors are preferably formed with CCDs in CMOS design. The light sources used are preferably lasers or laser diodes.

In the case of a first embodiment of the scattered light measuring device is provided that the coupling-out device is formed with a partially transmissive mirror which is tilted at an angle γ of about 45 ° to the main optical axis. As a result, the secondary beam is coupled out at an angle of 90 ° from the main beam of the scattered light measuring device.

In an advantageous embodiment of the first embodiment it is provided that the filter device is formed with a diaphragm which is arranged between the fourth convergent lens and a fifth converging lens in the secondary beam. This results in a structurally particularly simple construction of the filter device. Alternatively, the filtering in the sense of sampling theorem can also be done on the second camera sensor.

According to a second embodiment of the scattered light measuring device, the decoupling device and the filter device are formed with a full mirror, which decouples only low-frequency portions of the main beam in the secondary beam. As a result, the structural design of the scattered light measuring device further simplified because the full mirror at the same time takes over the task of beam splitting as well as the function of the filter device. The mirror itself acts as a Fourier filter due to its local boundary. In addition, in comparison to the first embodiment, a converging lens is less necessary in the secondary beam path.

According to a favorable technical development of the full mirror is convex or concave and tilted at an angle of about 45 ° to the main optical axis. As a result, the secondary beam extends at an angle of approximately 90 ° with respect to the main beam or to the main optical axis of the scattered light measuring device.

In a further advantageous embodiment, it is provided that the full mirror has a circular peripheral contour or an elliptical peripheral contour. As a result, the cross-sectional geometry of the secondary beam coupled out of the main beam can be influenced. In the case of the preferred elliptical peripheral contour, the projection results in a circular "entrance pupil" in the secondary beam.

In the case of a further embodiment, it is provided that a diameter or half-axes of the mirror is smaller than a diameter of the first lens in the main beam. As a result, the filter function of the solid mirror is made possible only because its cross-sectional area is significantly smaller than a cross-sectional area of the main jet in this area.

According to a further favorable development, an angle α between the sample surface and the main optical axis approximately corresponds to an angle β between the first camera sensor of a minor optical axis of the secondary beam. As a result, the observance of the s. G. Guaranteed "Scheimpflug" principle.

In accordance with a further advantageous refinement, the first and / or the second camera sensor are connected to a suitable electronic, digital evaluation unit and to an optical display unit, in particular a screen, in order to obtain measured data. This makes possible a complex, automatic numerical evaluation of the image data supplied by the camera sensors. For example, both images can be interpreted individually and the results can be assigned to specific frequency ranges. In addition, the measurement data z. B. are combined in the frequency domain, the scattering image undergoes a normalization of the frequency axis and the result of a self-folding is subjected.

In addition, the object of the invention is achieved by a method with two alternative methods, according to which a separate evaluation of the scattering image and the original image, in particular by means of suitable image processing algorithms of the evaluation, or the original image of a spectral analysis and the scattering image of a normalization is subjected, the result the spectral analysis and the result of standardization to a broadband spectrum for further processing and interpretation is summarized. As a result, in the case of the first variant of the method, a particularly simple evaluation method is provided in which, in addition, known analysis algorithms and means can be used.

On the basis of the fusion of the measurement data supplied by the two camera sensors as part of the second method alternative, compared to the separate evaluation of the measurement data according to the first alternative method further knowledge about the nature of the sample surface of the sample can be obtained.

An essential aspect of both process alternatives is the fact that the spectrum of the original image is obtained from the square of the field distribution in the image and therefore is related to the power density spectrum obtained from the scattering image via a self-folding. Accordingly, in the simplest version, the conditioning must emulate this self-folding in order to obtain fusible measurement data.

In the drawing shows:

1 A first embodiment of a scattered light measuring device,

2 a second embodiment of a scattered light measuring device, and

3 a schematic representation of the flow of a second process variant.

In the drawing, the same constructive elements each have the same reference number.

The 1 illustrates a first embodiment of the scattered light measuring device according to the invention.

The first embodiment of the scattered light measuring device 10 includes, among other things, a light source 12 for irradiation of a sample surface 14 a sample 16 with a parallel light beam 18 ,

As a light source 12 Preferably, a laser or a laser diode is used. The sample 16 is here merely exemplary at an angle α of 90 ° with respect to a main optical axis 20 aligned. Along the main optical axis 20 are each spaced from each other and one behind the other a first convergent lens 22 , a second condensing lens 24 , a third condenser lens 26 and a first plate-shaped camera sensor 28 arranged. The second and the third condenser lens 24 . 26 represent a known from the optics 4f system.

Between the second and the third condenser lens 24 . 26 there is a partially transparent mirror 30 , which by an angle γ of here exemplarily 45 ° with respect to the main optical axis 20 is arranged tilted.

That from the light source 12 emitted parallel light beams 18 falls at an acute angle to the sample surface 14 the sample 16 , resulting from the sample surface 14 a main beam 32 is thrown back. The sample 16 this is in a first focus 33 the first condensing lens 22 , The main beam 32 passes through the two collecting lenses 22 . 24 and falls on the semitransparent mirror 30 , Using the semitransparent mirror 30 then becomes the main beam 32 in a secondary beam 34 and a residual beam 36 divided up.

An optical minor axis 38 of the secondary beam 34 runs at right angles to the main optical axis 20 of the main beam 32 , The rest beam 36 retains the original orientation of the main beam 32 at and continues to run along the main optical axis 20 where he after passing through the last, third condenser lens 26 on the first camera sensor 28 hits and there is a scattering pattern 40 from the sample surface 14 generated, as the scattering image 40 already in the second focus 41 the first condensing lens 22 is included.

The with the help of the partially transparent mirror 30 from the main beam 32 decoupled or deflected secondary beam 34 goes through a fourth converging lens 42 , a panel 44 , one of these fifth condensing lens 46 and then falls at an angle β of 90 ° to a second camera sensor 48 , The fourth lens 42 , the aperture 44 , the fifth lens 46 and the second camera sensor 48 lie in each case on the optical minor axis 38 , wherein the fourth and the fifth convergent lens 42 . 46 form a 4f system. On the second camera sensor 48 the original picture is created 50 a lighting spot 52 from the light beam 18 on the sample surface 14 arises. The illumination spot 52 corresponds to one by means of the scattered light measuring device 10 metrologically detectable scanning zone or a measuring field on the sample surface 14 ,

One from the sample 16 outgoing and higher frequencies containing diffraction order 54 is due to the effect of the partially transmissive mirror 30 in the two diffraction orders 55 and 56 disassembled. With the help of the aperture 44 Low pass filtering or frequency limitation in the secondary beam takes place 34 , In the illustrated embodiment of 1 is thus the semi-transparent mirror 30 reflected and higher frequencies containing diffraction order 56 using the aperture 44 from the minor ray 34 hidden or completely suppressed, while a diffraction order containing lower frequencies 57 of the main beam 32 both the semi-transparent mirror 30 as well as the aperture 44 passed unhindered and to create the original image 50 serves.

The result is in the secondary beam 34 a limitation on low-frequency components in the light source 12 emitted light beam 18 while in the rest beam 36 especially its high-frequency components remain.

The partially transparent mirror 30 forms in this first embodiment, a decoupling device 58 while the aperture 44 a filter device 60 represents in the technical sense. Furthermore, in order to adhere to the so-called "Scheimpflug" principle, the angles α, β should always be the same irrespective of the value of 90 ° chosen here only for illustration purposes. For the first camera sensor 28 to reproduce the spread image 40 arise in the case of a deviating from the rectangular orientation arrangement of the sample 16 in relation to the main optical axis 20 no consequences.

2 shows a second embodiment of a scattered light measuring device according to the invention.

The structure of the scattered light measuring device 70 according to the second embodiment largely follows the structure of the scattered light measuring device 10 to 1 , This is how the sample surface becomes 14 the sample 16 again from the light source 12 with a parallel (coherent) light beam 18 irradiated and the sample 16 , the collecting lenses 22 to 26 as well as the first camera sensor 28 are again spaced from each other along the common optical axis 20 aligned, focusing on the camera sensor 28 again the spreading pattern 40 the sample surface 14 maps.

In contrast to the first embodiment, the scattered light measuring device 70 about one at an angle γ with respect to the main optical axis 20 tilted arranged full mirror 72 which is in an area between the first condenser lens 22 and the second condenser lens 24 symmetrical to the main optical axis 20 is positioned. The term "full mirror" defines in the context of this application that on the full mirror 72 incident radiation is almost lossless or 100% reflected in the ideal case. The angle γ is merely exemplary 45 ° and can if necessary. have different values.

Using the full-size mirror 72 takes place in a region between the first and the second condenser lens 22 . 24 a decoupling of a secondary beam 74 from the main beam 32 , where the secondary beam 74 along the optical minor axis 38 runs at right angles to the main optical axis 20 is arranged. At the same time by means of the full-size mirror 72 in the secondary beam 74 a limitation or a filtering on low-frequency components or on low-frequency diffraction orders 57 of the main beam 32 while the high-frequency diffraction orders 54 in the main beam 32 the full mirror 72 can pass unimpeded laterally.

By the secondary beam 74 creates an original picture 76 of the illumination spot 52 on the second camera sensor 48 , To the targeted decoupling of the low-frequency diffraction orders 57 from the main beam 32 to allow, is a horizontally projected diameter 78 of the full-size mirror 72 smaller than a diameter 80 the front, first condenser lens 22 , To a circular cross-sectional geometry of the secondary beam 74 To achieve the full mirror 72 a deviating from the circular geometry, in particular an elliptical peripheral contour, have. After the secondary beam 74 from the main beam 32 by means of the full-size mirror 72 is decoupled, this passes through the last, fifth convergent lens 46 and hits the camera sensor 48 on.

In the full mirror 72 are thus with only one component, the functions of a decoupling device 82 and that of a filter device 84 realized, resulting in comparison to the first embodiment, a simplified structural design.

Because of the full mirror 72 In addition to its actual beam deflection function inherent filter effect, low-frequency components are found in the of the light source 12 emitted radiation in the secondary beam 74 again, whereas in the rest beam 36 that's over from the collecting lenses 24 . 26 existing 4f system on the first camera sensor 28 falls, only the remaining high-frequency components are included. As a result, at the same time direct reflections from the scattering image 40 hidden, so that an otherwise necessary beam trap (so-called "beam dump") can be omitted. In addition, the full mirror can 72 itself be designed as a convex or concave mirror, so that u. U. the fifth condenser lens 46 Can be omitted and the structural design of the scattered light measuring device 70 further simplified.

To comply with the "Scheimpflug" principle, the two angles α, β are between the sample 16 and the main optical axis 20 or between the second camera sensor 48 and the minor axis 38 also the same size.

In the further course of the description, a first variant of the method for evaluating the measurement data or the images supplied by the two camera sensors of the scattered light measuring device will first be briefly explained. In this process variant, a separate evaluation of the original image 50 and the scattering image 40 ie an independent image evaluation of the two camera sensors 28 . 48 supplied image information.

For this purpose, the original image 50 evaluated by means of conventional methods of image processing and, for example, examined for defects such as scratches, etc. The results can be determined by means of suitable image processing algorithms z. B. directly to the original image 50 , in particular in the form of visual markings, are superimposed. As a result, the recognizability of any defects on the sample surface to be examined 14 facilitated. From the scattered image analyzed separately 40 however, z. As main directions and penetration depths of processing tracks, preferred directions, as well as spatial frequencies of periodic structures in the sample surface 14 and their orientation and course are derived. Furthermore, if required, roughness parameters of the sample surface 14 be derived from the moments of the scattering distribution in a method familiar to the skilled person from the prior art methodology.

Based on the schematic representation of 3 the sequence of a second variant of the method, ie the integrative evaluation of the measurement data supplied by both camera sensors, will be explained in more detail.

The of the two camera sensors 28 . 48 supplied measurement data 90 . 92 or image information becomes an evaluation unit 94 supplied, which is preferably a fast electronic digital computer 96 , such as a PC or the like.

In the course of this second variant of the method, that of the measured data 90 of the first camera sensor 28 represented original picture 50 by means of the evaluation unit 94 a spectral analysis 98 subjected. That from the measurement data 92 embodied scattered picture 40 of the second camera sensor 48 is in the evaluation unit 94 a normalization 100 subjected in the frequency domain. In conclusion, results 102 . 104 from the spectral analysis 98 and standardization 100 by means of a suitable algorithm to a broadband spectrum 106 summarized, then for further processing and interpretation as the final result 108 ready. The final result 108 For example, it may be visualized to a viewer on a suitable output device, such as a screen or monitor. A if necessary. subsequent further processing and interpretation of the final result may also preferably by means of the evaluation unit 94 made and allows detailed findings regarding the nature of the sample surface, which have already been set out above in the description of the first method variant.

An essential aspect of the second process variant is the fact that the spectrum of the original image 50 is obtained from the square of the field distribution and therefore with that from the scattering image 40 gained power density spectrum is related to a so-called "self-folding". Correspondingly, therefore, in the simplest version must be the conditioning in the context of standardization 100 simulate this self-folding, to fusible or mergeable measurement data 90 . 92 to obtain.

LIST OF REFERENCE NUMBERS

10

Scattered light measurement device

12

light source

14

sample surface

16

sample

18

parallel light beam

20

main optical axis

22

first condensing lens

24

second condenser lens

26

third condenser lens

28

first camera sensor

30

semitransparent mirror

32

main beam

33

1st focal point (1st lens)

34

secondary beam

36

rest beam

38

optical minor axis

41

2nd focal point (1st lens)

40

spreading pattern

42

fourth condenser lens

44

cover

46

fifth condenser lens

48

second camera sensor

50

original image

52

illumination spot

54

Diffraction order (HF)

55

Diffraction order (HF)

56

Diffraction order (HF)

57

Diffraction order (NF)

58

decoupling device

60

filtering device

70

Scattered light measurement device

72

full mirror

74

secondary beam

76

original image

78

Diameter (full mirror)

80

Diameter (1st convergent lens)

82

decoupling device

84

filtering device

90

measurement data

92

measurement data

94

evaluation

96

elec. digital computer

98

spectral analysis

100

standardization

102

Result (spectral analysis)

104

Result (normalization)

106

Result (spectral analysis)

108

end result

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009036383 B3 [0004]

Claims (10)

Scattered light measuring device ( 10 . 70 ) with a first camera sensor ( 28 ) with at least three upstream converging lenses ( 22 . 24 . 26 ) and a light source ( 12 ) for illuminating a sample surface ( 14 ) of a sample to be examined ( 16 ) with a parallel light beam ( 18 ), whereby the sample ( 16 ), the at least three converging lenses ( 22 . 24 . 26 ) as well as the first camera sensor ( 28 ) in each case spaced apart along a common optical axis ( 20 ), characterized in that at least a part of one of the sample surface ( 14 ) outgoing main beam ( 32 ) by means of a decoupling device ( 58 . 82 ) and a filter device ( 60 . 84 ) into a secondary beam ( 34 . 74 ) for transmitting an original image ( 50 . 76 ) of the illumination spot ( 52 ) to a second camera sensor ( 48 ) and a residual jet ( 36 ) for the transmission of the spread image ( 40 ) of the sample surface ( 14 ) to the first camera sensor ( 28 ), whereby the original image ( 50 . 76 ) predominantly low-frequency components and the scattering pattern ( 40 ) contains substantially high-frequency components and the second camera sensor ( 48 ) at least one fourth converging lens ( 42 ) is connected upstream. Scattered light measuring device ( 10 ) according to claim 1, characterized in that the coupling-out device ( 58 ) with a partially transparent mirror ( 30 ) formed at an angle γ of about 45 ° to the main optical axis ( 20 ) is arranged tilted. Scattered light measuring device ( 10 ) according to claim 2, characterized in that the filter device ( 60 ) with an aperture ( 44 ) formed between the fourth converging lens ( 42 ) and a fifth converging lens ( 46 ) in the secondary beam ( 34 ) is arranged. Scattered light measuring device ( 70 ) according to claim 1, characterized in that the decoupling device ( 82 ) and the filter device ( 84 ) with a full mirror ( 72 ) are formed, the only low-frequency components of the main beam ( 32 ) in the secondary beam ( 74 ) decoupled. Scattered light measuring device ( 70 ) according to claim 4, characterized in that the full mirror ( 72 ) is convex or concave and at an angle of about 45 ° to the main optical axis ( 20 ) is arranged tilted. Scattered light measuring device ( 70 ) according to claim 4 or 5, characterized in that the full mirror ( 72 ) has a circular peripheral contour or an elliptical peripheral contour. Scattered light measuring device ( 70 ) according to claim 6, characterized in that a diameter ( 78 ) or half-axes of the full-size mirror ( 72 ) smaller than a diameter ( 80 ) of the first lens ( 22 ) in the main jet ( 32 ) are. Scattered light measuring device ( 10 . 70 ) according to one of the preceding claims, characterized in that an angle α between the sample surface ( 14 ) and the main optical axis ( 20 ) at approximately an angle β between the second camera sensor ( 48 ) of an optical minor axis ( 38 ) of the secondary beam ( 34 ) corresponds. Scattered light measuring device ( 10 . 70 ) according to one of the preceding claims, characterized in that for the acquisition of measured data ( 90 . 92 ) the first and / or the second camera sensor ( 28 . 48 ) with a suitable electronic, digital evaluation unit ( 94 ) and with an optical display unit, in particular a screen, are connected. Method for evaluating measured data ( 90 . 92 ) using the scattered light measuring device ( 10 . 70 ) in accordance with at least one of claims 1 to 9, characterized in that a separate evaluation of the scattering pattern ( 40 ) and the original image ( 50 . 76 ), in particular by means of suitable image processing algorithms of the evaluation unit ( 94 ), or that the original image ( 50 . 76 ) of a spectral analysis ( 98 ) and the spread of normalization ( 100 ), the result of the spectral analysis ( 98 ) And the result ( 104 ) of standardization ( 100 ) to a broadband spectrum ( 106 ) is summarized for further processing and interpretation.

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